Containers having liquid dispenser assemblies secured thereto are well known. U.S. Pat. No. 5,730,335 discloses a liquid dispenser including a precompression system. This liquid dispenser is a trigger sprayer having a sprayer housing that may be fixed onto the neck of a container. The sprayer housing contains a manually operated pump. An operating element in the shape of a trigger as pivotally connected to the housing for operating the pumb. A dip tube may extend from the pump and into the container so that the liquid in the container may be drawn through the dip tube and into the pump during operation thereof. The trigger sprayer also includes an outlet in fluid communication with the pump for discharging the fluid. The trigger sprayer further includes a spring located in the pump for biasing the piston of the pump to return to a charged position at the end of a discharging pump stroke.
The precompression system of this prior art trigger sprayer serves to prevent liquid from leaving the outlet at too low a pressure, which would result in insufficient atomization of the liquid with large drops of fluid or liquid being formed in the spray pattern. The precompression system includes a precompression valve moveable between a position that closes off communication between the pump and the outlet and an open position in which it is spaced from a valve seat for opening communication between the pump and the outlet. The precompression valve is a shallow dome made of a spring material, such as stainless spring steel or a stiff but resilient plastic material. It is biased toward a closed position, in which its convex side engages the valve seat, by its inherent spring characteristics. The precompression valve is flexed to its open position only when a predetermined pressure is attained within the pump.
Among the problems associated with this prior art liquid dispenser and its precompression system are the large number of separate parts, which moreover are made from different materials, and the sometimes irregular dispensing pressures achieved by the precompression system.
The high number of parts results in a product that is both difficult to manufacture and assemble. As a result, both the manufacturing and the assembly of the dispenser parts are expensive and time consuming. In addition, the different materials pose problems in handling and recycling the trigger sprayer and the container when the items are ready to be discarded. For example, the metal spring used for returning the piston and the stainless steel spring valve must both be removed from the trigger sprayer before the plastic portion of the item may be recycled.
The variations in the pressure that is built up in the prior art precompression system is due to the fact that the convex side of the dome shaped spring valve is moved away from the valve seat by flexing the valve such that it assumes a somewhat “wavy” shape in cross section. This is an unstable situation, which may lead to the same amount of pump pressure resulting in varying deformation and consequently varying degrees of opening of the coring valve. Moreover, there is a risk that the spring valve may abruptly snap to an inverted position, thus leaving an open connection between the pump and the outlet.
In response to the above problems, commonly assigned U.S. Pat. No. 6,378,739 discloses another liquid dispenser which includes a precompression system. In this prior art liquid dispenser, which has generally the same functionality and structure as the dispenser of the '335 patent discussed above, both the number of separate parts and the use of different materials is reduced in comparison to the liquid dispenser of the '335 patent. To this end the springs for returning the piston at the end of a pump stroke are made from a plastics material and are integrally molded with the neck of the container. Moreover, the precompression system of this brier art liquid dispenser includes a precompression valve that is made of a plastics material as well and that is integrally molded with a sleeve which mounts the valve in a valve chamber. This extensive, use of integrally molded plastic structures limits the number of separate parts, resulting in a liquid dispenser that is easy to manufacture and assemble. Moreover, handling and recycling of the liquid dispenser when it is discarded after use is facilitated.
The precompression valve of the liquid dispenser disclosed in the '739 patent includes a dome shaped elastic diaphragm that engages the precompression valve seat with its convex side. Therefore, this elastic diaphragm is still prone to inversion when subjected to pump pressure. In order to limit the amount of deflection of the diaphragm and prevent it from being moved to an inverted position, a stop member protrudes from the concave side of the diaphragm towards a fixed part of the dispenser housing. Nevertheless, the degree to which the diaphragm deflects when the pressure in the pump increases and consequently also the valve opening may vary.